Astable multivibrator

ABSTRACT

A multivibrator circuit comprising a base bias-supplying circuit for a transistor which is connected with at least one diode in parallel with a resistor for obtaining stable temperature and voltage characteristics. This resistor serves to overcome the problem of the cessation of variations in bias voltage directly proportional to the supply voltage which is caused by the insertion of the diode. Thus it is possible to start and stop oscillation of the multivibrator circuit even when the supply voltage is reduced to a considerably lower voltage.

United States Patent [151 3,670,264 Wakai [4 1 June 13, 1972 [s41ASTABLE MULTIVIBRATOR [56] Mm CM [72] inventor: Shuzo Wakal, Kyoto,Japan I OTHER PUBLICATIONS Temperature Dependence in Multivibrators"Electro- Magnet Mlmuhm Elem-om C I Technology, W. F. Miller, August 1964Pgs. 38- 4l, I54.

. Osaka, Japan 22 Filed; M 22, 1971 Primar 'Examiner-John KominskiAnorneyStevens, Davis, Miller & Mosher [2]] App]. No.: 126,458

g [57] ABSTRACT [30] Foreign A liution Priority Data 1 A multivibratorcircuit comprising a base bias-supplying circuit for a transistor whichis connected with at least one diode March 27, 1970 Japan ..45/2635l inparaud with a resistor f obtaining u temperature and voltagecharacteristics. This resistor serves to overcome the ['52] U.S. Cl....33l/l 13 R, 331/ 176 problem of the cessation of variations in biasvoltage directly [51] In 03k 3/232 proportional to the supply voltagewhich is caused by the in- Searc .331 113, 176 dim-11mm mime and POscilla- [58] Field of h tion of the multivibrator circuit even when thesupply voltage is reduced to a considerably lower voltage.

1 Claim, 4 Drawing Figures PATENTEBJUH 13 m2 3, 70,2

, 2 mm.anr F161 4 0 VC6--- Vac-.-

Jfwm/ INVENTOR ATTORNEY The present invention relates to a circuit forreducing oscillation starting and stopping-voltages for an emittercapacitorcoupled multivibrator circuit.

The emitter capacitor-coupled multivibrator circuit presents a problemof temperature and voltage characteristics in which an oscillatingfrequency is subject to variations of supply voltage and ambienttemperature. To overcome this problem, conventional devices have one ormore'diodes connected in series with a resistor in a bias circuit.

Objects, features and advantages of the present invention will becomeapparent from the following detailed description of the preferredembodiments taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a diagram showing a conventional emitter capacitor-coupledmultivibrator circuit with improved temperature and voltagecharacteristics of oscillation frequency;

FIG. 2 shows a diagram for explaining the relationship between thesupply voltage and bias voltage of the astable multivibrator circuit ofFIG. 1;

FIG. 3 is a diagram showing an emitter capacitor-coupled multivibratorcircuit according to the present invention; and

FIG. 4 shows a diagram for explaining the relationship between thesupply voltage and bias voltage of the multivibrator circuit of FIG. 3.

Referring to FIG. 1 of the conventional multivibrator, numerals l and 2show oscillating transistors, numerals 3 and 4 resistors for determiningan oscillation frequency, numeral 5 a coupling capacitor, numeral 6 acollector resistor, numerals 7 and 8 resistors for supplying a basebias, numerals 9 and 10 terminals for supplying a DC voltage, andnumeral 11 diodes for improving the temperature and voltagecharacteristics.

The provision of the diodes in the base bias supplying circuit causesimproved temperature and voltage characteristics due to the constantvoltage drop across the diodes 11, but the bias voltage V at thejunction point 12 between resistors 7 and 8 is not directly proportionalto the supply voltage V Such a relation is shown in FIG. 2, from whichit is apparent that, in the absence of the diodes, the supply voltage Vis directly proportional to the bias voltage V, as shown by the straightline A, whereas, with the diodes 11 inserted, the voltage at thejunction point 12 is raised by the amount V which is determined by theproduct of the number of the diodes inserted and the forward voltage ofeach of the diodes, resulting in the voltage at the junction point 12 asshown by the dotted line B. Here, it is needless to say that theresistance value of the resistor 7 or 8 is different from that in theabsence of the diodes since the base of the transistor 2 should bealways supplied with a predetermined constant voltage corresponding tothe intersecting point of both the full and dotted lines in FIG. 2,whether the diodes 11 are connected to the circuit or not. It followsthat with the increase in the number of the diodes inserted, the voltageV at the junction point 12 is decreased at a lower rate. If the voltageV is reduced smaller than the value at the intersecting point, the basevoltage V of the transistor 2 becomes larger by inserting the diodes inthe circuit, which results in biasing the transistor in the forwarddirection, detriorating the oscillation capability thereof and therebyinconveniently increasing the voltages needed for starting and stoppingthe oscillation.

The present invention is aimed at obviating the problem of the highoscillation startingand stoppingvoltages caused by the diodes which areinserted in the base bias-supplying circuit for compensating for theinfluence of the ambient temperature and supply voltage on theoscillation frequency, and is characterized by a resistor shunted withthe diodes in the base 2 bias-supplying circuit.

Explanation will be now made of the present invention with reference toFIGS. 3 and 4. FIG. 3 is a circuit diagram of an emittercapacitor-coupled multivibrator according to an embodiment of theinvention, in which a resistor 13 is connected in shunt with the diodes11. The presence of the resistor 13 eliminates the problem caused by thediodes. In other words, when the supp y voltage V, rs normal, the basebias voltage (the voltage at the junction point 12) of the transistor 2is maintained at a value determined by the voltage drop in the forwarddirection through the diodes 11 and resistors 7, 8 and 13.

When the supply voltage is decreased, the voltage across the resistor 13also decreases. As long as this voltage across the resistor 13 is higherthan the forward voltage drop of the diodes 11, a current flows in thediodes l1 and the voltage between the junction point 14 and terminal 10is controlled by the amount of the forward voltage drop in the diodes,thus compensating for the variations in oscillation frequency caused byvariations in temperature or voltage.

However, when the supply voltage V is further reduced to the point wherethe above-mentioned relation is not maintained, that is to say, thevoltage across the resistor 13 is decreased more than the forwardvoltage drop across the diodes 11, the absence of the resistor 13 causesthe voltage V at the junction point 12 to decrease straight along thedotted line of FIG. 4 toward the point V having a greater effect on theconduction of transistor 2, with the result that the loop gain isreduced and the oscillation stops at a certain higher supply voltage.The insertion of the resistor 13, however, causes the diode 11 to becut-off at such a reduced value of the supply voltage as is insufficientto maintain the abovernentioned relation. As a result, the current pathalong the diodes 11 is virtvally opened, and the voltage V at thejunction point 12 which is subsequently controlled by the resistors 7, 8and 13 follows the full line to zero as shown in FIG. 4.

The relationship between the supply voltage V and voltage V at thejunction point 12 in the multivibrator circuit according to the presentinvention is as shown by the solid line C of FIG. 4. This multivibrator,unlike the conventional one in which V follows the dotted line frompoints X to V maintains oscillations until a lower supply voltage isreached, since the reduction in loop gain due to the saturation oftransistor 2 is less.

Not only in the stoppage of oscillation but in starting the oscillationdoes the multivibrator according to the present invention achieve alower voltage than does the conventional multivibrator. In other words,the voltage at the junction point 12 increase along the solid line Ceven when the supply voltage V rises from zero.

It will be understood from the above description that the multivibratorcircuit according to the present invention makes it possible to startand stop oscillations at a lower voltage than the conventionalmultivibrator circuit. For this reason, the multivibrator circuitaccording to the present invention is suitable for application to ahorizontal oscillator circuit of a television receiver which requireslower starting and stopping voltages than a vertical oscillator circuit.

What is claimed is:

1. A multivibrator circuit comprising an emitter capacitorcoupledmultivibrator circuit including two switching transistors with emittersconnected with each other through a capacitor, the base of one of saidswitching transistors being connected with a base-biasing meanscomprising a plurality of dividing resistors and at least one diodeconnected in series with one of said dividing resistors, said diodebeing connected in parallel with a resistor.

1. A multivibrator circuit comprising an emitter capacitorcoupled multivibrator circuit including two switching transistors with emitters connected with each other through a capacitor, the base of one of said switching transistors being connected with a base-biasing means comprising a plurality of dividing resistors and at least one diode connected in series with one of said dividing resistors, said diode being connected in parallel with a resistor. 